This invention relates to a rotation transmission device for transmitting a torque with a torque limiting function, and more particularly to such a device with a purely mechanical torque limiting transmission mechanism.
Conventionally, torque limiting transmission devices utilize, as the torque limiting transmission means, friction, viscosity or dynamic pressure of a fluid, or an electromagnetic force. While the magnitude of the load acting on the output shaft is below a predetermined maximum, a torque equal to the load is tranmitted from the input to the output shaft. However, when the load exceeds the predetermined maximum, the input shaft slips relative to the output, thereby limiting the torque of the output shaft under the predetermined maximum.
The conventional torque limiting transmission devices have the following characteristics: First, throughout during the torque limiting mode operation, the input shaft slips relative to the input shaft. Second, also throughout the torque limiting mode operation, the torque equal to the torque limiting value (the predetermined maximum) act on the input as well as the output shaft.
Thus, the conventional device has the following problems. Namely, within the torque limiting transmission is generated a power loss equal to the product of the predetermined maximum torque limiting value and the relative slipping rotational velocity between the input and the output shafts. Almost all the power loss is converted into thermal energy, and raises the temperature of the component parts in the neighborhood. Thus, measures should be taken to prevent the deformation or degeneration of the parts of the torque limiting transmission means. Further, there arises the problem of the function or performance that, due to the temperature rise, the maximum torque limiting value or the operational durability vary unstably.